A multi-technique study of CO2 adsorption on Fe3O4 magnetite

J. Pavelec, J. Hulva, D. Halwidl, R. Bliem, O. Gamba, Z. Jakub, F. Brunbauer, M. Schmid, U. Diebold, G.S. Parkinson

Institut für Angewandte Physik, Technische Universität Wien, 1040 Wien, Austria

J. Chem. Phys. 146 (2017) 014701

The adsorption of CO2 on the Fe3O4(001)-(√2×√2)R45° surface was studied experimentally using temperature programmed desorption (TPD), photoelectron spectroscopies (UPS and XPS), and scanning tunneling microscopy (STM). CO2 binds most strongly at defects related to Fe2+, including antiphase domain boundaries in the surface reconstruction and above incorporated Fe interstitials. At higher coverages, CO2 adsorbs at fivefold-coordinated Fe3+ sites with a binding energy of 0.4 eV. Above a coverage of 4 molecules per (√2×√2)R45° unit cell, further adsorption results in a compression of the first monolayer up to a density approaching that of a CO2 ice layer. Surprisingly, desorption of the second monolayer occurs at a lower temperature (~84 K) than CO2 multilayers (~88 K), suggestive of a metastable phase or diffusion-limited island growth. The paper also discusses design considerations for a vacuum system optimized to study the surface chemistry of metal oxide single crystals, including the calibration and characterisation of a molecular beam source for quantitative TPD measurements.

Corresponding author: Gareth S. Parkinson (parkinson at iap_tuwien_ac_at).

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